JP 2013-20289-A, JP 2008-174605-A, JP 2009-191116-A, JP 2010-163536-A and WO 2014/021315 disclose technologies to form a product having a desirable shape by heating and pressing fiber-reinforced forming material comprising bundled aggregate of discontinuous reinforcing fiber, such as carbon fiber, and matrix resin, such as thermosetting resin. When such a conventional fiber-reinforced resin forming material comprises fiber bundles consisting of a predetermined strand containing many single yarns, a formed product tends to have poor mechanical properties in spite of excellent fluidity in forming.
JP 2013-20289-A discloses a forming material of which chopped fiber bundle has a filament number of 10,000-700,000. Although such a forming material may have an excellent fluidity derived from many pieces of filaments of fiber bundles to allow the fiber bundles of reinforcing fiber to move efficiently with resin in a forming process, the formed product might be broken as generating stress concentration at ends of fiber bundle in the formed product and, therefore, such a forming material is not suitable for forming a formed product requiring high level mechanical properties.
JP 2008-174605-A discloses a fiber-reinforced resin made from split fiber bundles having 100 or less pieces of single yarns. Although such a fiber bundle having less pieces of single yarns than the single yarns of JP 2013-20289-A can disperse reinforcing fiber well in the formed product to enhance mechanical properties of formed product because of decreased possibility to generate stress concentration at ends of fiber bundle in the formed product, the fluidity might not be greater than expected in the forming process.
As described above, a fiber-reinforced resin forming material made from fiber bundles having many pieces of single yarns tends to have a good productivity and an excellent fluidity in a forming process in spite of poor mechanical properties. Adversely, a fiber-reinforced resin forming material made from fiber bundles having less pieces of single yarns tends to have excellent mechanical properties of the formed product in spite of suppressed fluidity in a forming process.
Accordingly, it could be helpful to provide a fiber-reinforced resin forming material and a method of producing the same capable of achieving both good fluidity in forming products and excellent mechanical properties of the product in a balanced manner.